Preparation of a dehydrogenation catalyst



Patented July 15, 1952 PREPARATION oEA DEHYDYRQOGENATIONH f CATALYST I H 1 James Lawrence Amos and Lloyd H. 'Silvernail," Midland, and Frederick J. Soderquist, Essex ville, Mich., assignors toJlhe, Dow Chemical Company, Midland,. Mich a corporation of Delaware This invention relates to an improvement in de hydrogenation and cracking catalysts produced: initially in ,pellet form, anduis concerned par-v ticularly with such catalyststas aresuitable for. the dehydrogenation of ethylbenz'ener to produce? monomeric styrene.' .v 7

Dehydrogenation catalysts are commonly made from one or a mixture of the oxides; especially the fdiflicultly reducible oxides, or oxygen-con taining'salts of such diverse metals as'alumi'num,

chromium, iron, nickel, cobalt, cerium, vanadium,= niobium (columbium), tantalum, tita'nium,'and

the like, often in admixture with an oxide or oxygen-containing. salt of lithium or potassium.

The tungstates, molybdates, silicates, carbonates, andsimilar salts have been employedin prepar ing" manyv dehydrogenation catalysts. The lit.-; erature is replete with suggestions to .usespecific mixturesjzascatalysts in specific dehydrogena-. tion reactions. The active, oxides; are commonly; bound together in a porous mass by a. cement.

which is often the agent which provides, also, the

aluminum or other oxide constituents of the; catalyst; Catalysts i for thermal cracking often; have similar compositions. It is (common prac f videv an improvement in pelleted catalysts for tice, to dissolve inorganicfsalts, which yield oxides when heated, in water and to stir thecementpr other binder and insoluble oxides into such solution until a uniform thick paste is obtained: The paste is often extrudedas a continuous rib: 3

bon or rod, and the latter is cut in suitableshort n ceslets have inadequate strengthand hardness after being dried at the suggested-80150 C.,-and-- that they are crumbled easily by;v attrition has been noted as wellthat, when heated to' rea tion temperature, they become still weaker, th

are notas permeable to the reagent vapors as" might be desired, and a means is'sought to im'- 111; hasfbeen jtheorize'd" thatf the, addition fofi The. resulting particles are still "moist, and are -dried, suitably at .80 15'0 C., to. remove; at'erand to complete" the 'settingoflthe 6e, entitious ,binder'. When required forfusef, in, a dehydrogenation reaction,'the ,pellets' are, heated to the intended freactiontemperature, l t'eferably'in a stream of steam and in an at? mo'sphere of the vapors or'gas to'be dehydro genated. It is common experience that such pel- No D1-awing. Application June 11, 1949,

Serial No. 98,636 4 Claims. (01. 252+470) i tentof the plastic-extrusion mix is its transition from plastic gel with a definite yield strength to a-fiuid with no yield strength. Evenif such fluid; can: be extruded, the product is not-a coherent ribbon or rod but spreads like a fluid upon emer gence from the orifice and merges with other such streams. vOnly non-coherent powdered catalyst, mixtures can be obtained by drying such a product'. In those cases in which the catalyst is ,activated in a stream of steam at the intended reac-,- tion tcmperature,.or in" which the reagent vapors; are heated and passed together with steam through the' catalystnbed, graphite 'and carbonblack have been put into the wet extrusion mix" to provide:additionalporosity in the final pellets, due to the voids left when the carbonis destroyed: by the water-gas reaction during preheating, ofthe catalyst. suchpellets are-found to-be quite, weak. 1 It is an object of the present invention to'procracking and dehydrogenation reactions, and, especiallyior the dehydrogenation of ethylben zene to styrene, whereby the'yield strengthand" coherence of the extruded wet "mix is improved; thed ry strength ofthe pellets is increased, a the efficiency of' the catalyst is improved! particular object is'to provide an improvement as: atoresaid in the type of catalyst useful in conv'ert- 'i ng, ethylbenzene to styrene, whereby: the 'tem-AI perature of dehydrogenation maybe lowered and the conversion of ethylbenzene to styrene in a single'pass through the catalyst bed may be in-'- creasedy-Related objects may appear hereinafter; p

We have found that the amount of water which} can bef'tolferatedf in one of the above suggestedfams e tr sign m xes a b increased a rial1y, and that" the extrusion characteristics of the mix maynevertheless be improved; by blend? ing tromj3'tof15 percent (preferably' 7 to 15 per cent) of methyl-cellulose therewith, provided that the methyl cellulose is one whose 2' per cent solu- V tion in water'at'20 C. hasa viscosity of fromBOQ'f to 7500 centipoises; and preferably from 2000 'to'" 3000 centipoises. Weha've found, further, that graphite or carbonjblack may be omitted from such a mixfif desired, but that, even when they areincluded, the strength of the oven-dried pellets'is greater when the methyl cellulose is present than without it, The wet extruded product con 'ation.

taining methyl cellulose does not form haircracks," either before or after baking, such as have been common heretofore. A more surprising result-is-obtained, however,when the baked pellets containing methyl cellulose are heated tothe intended reaction temperature in a stream of the vapors to be dehydrogenated. The resultingq I catalyst, even after prolonged operation, is harder than an otherwise identi-cal'pell'et' without.

methyl cellulose. At reaction temperature, an

other and entirely unexpected-'result is obtained. 1

The pellet is more porous and::rtiore permeable to the reagent vapors than '="on'e made without I methyl cellulose, and it is found th at a higherconversion to dehydrogenated product is obtained, and at a significantly lower: temperature,

than when the same catalyst made without meth yl cellulose is used. When it is considered that the methyl cellulose is no longer present-inthe catalyst pellets at dehydrogenation temperatures, sin'ce'it has been destroyedtby exposure to such. heatZ -the increased effectiveness oithe catalyst is diifi'oult to explain, 'and we do' not advance any" spec'ific theoryin explanationithereof.

The invention will be: illustratedlby means. of:

the following examples 5 showing i the preparation and properties' of catalysts used in the" cohver-' siori ot ethylbe'nzene to styrene by dehydrogen- In e'a'ch eases-100 parts-of the designatedsolids and-the: stated number of-parts of water were.

used in' making the" extrusionmix; The: soluble salts i (usually carbonate and dichromate) were dissolved the water and the remaining solids were: thoroughly mixed with the solution to form;

a si nooth paste, which. wasextrudedras rods,

{e m ch m diameter andjcut to'fi inch lengths. Thewet pel lets were dried at.l'25 C'. and their crushing: strength. was measured between *tvvo' smoothcement 'was' a comrnercial slow-"setting. cor rosion resistant-g refractory cern'er t having the following proximate analysis;

1 Per cent Ins The methyl cellulose us'ed' 'in the mixtures reported below was-one whose 2 per cent solution in water at 20 C. had a viscosity of 400 ce'r'itii .poises. -'I-he dried. pellets were used to fill a reactortube through which ethylbenzene .vapor could be passed and. in. which the temperature c uIdbe controHed atthe minimum value-at.

which dehydrogenation tofs'tyrenelwas' found to occur. Ethylbnz'en'e was mixed 'vv-ith stam and' passed over. the-pellets at anthem temperature of 6'5'0-C which te'mperature was gradually lowered to the reported operating temperature;

the latterlbeing chosen. to give a standard ie-per cent conversion'to styreneper pass. 'Ihev amount;

of .by-products (chiefly benzene and. toluene.)

rome'd,, and the yield off'styr'ene, based on the, conversion, were determined-" -'I 1'1e-data-'reported below arethose for thel'fi'fthfday of operationwith eachlcatly st. Experience has s'how-n tllafi the catalysts'of this type (Without methyl 661- late's. -The constituent designated as;

lulose) are capable of operating for as long as two years.

l Proportions =Used Catalyst Constituents Control A B C Me'th'y1 cellulose; 0.0 5.0 10.0 15.0 Potassium carbonate... 2. 8 2.9 2. 9 2. 9 Potassium dichromate 10. 8 10.4 10.4 10. 4 l1. 4 11. 3 11.2 11.2 22. 0 l9. 9 l5. 0 10. 0 53.0 50. 5 50. 5 50.5 v l6. 2 33. 3 25. 9 26. 8

Results Crushing strengthbaked pellets,

lbs 27 32 23 By-pro duct, per cent. 2. 4 3. 7 2. 3 2. 5 Conversion to styrene; per cent 40. 2 40. 4 41. 6 41. 8 iYleld'of styrene, per cent 89.8 87. 4 89. 5 89.3

Minimum operating temperature, for 40 percent conversion, C 630 610 610 615 1 Not measured.

It observed that the'pellets containing methyl. 7

cellulose even with their .initial higherwater content, had strengths comparable to that. 'of. theiblank, and thatsm'aller amounts ofigraphite were employed in extruding the methyl cellulose mixtures. This was-accomplished without. developing hair cracks in the extruded product. Theoperating temperature, for comparable or slightly higher conversion rates to styrene, was

15 to1 20.,centigrade degrees lower when using the new mixture than when: using the: standard catalyst,

When the typeofJmethyI cellulose Was changed I to a grade whoser2 per cent solutioni'in water-at room temperature had. a viscosity in therange from 2000 to 3000 centipoises,-the catalyst peblots were strongenwhen baked, having crushing range from-5. 150115 percent. In contrast,'the pellets produced usinglow viscosity methyl eel"- lulose.hadcrushingstrengths of the order of 4- to 5 pounds after a weekat 610 to 620 in the dehydrogenation zone; It has been'found desirable,- to" avoid formation of excess powder by attrition, for the catalyst pellets to havecrushing strengthsy-after a week sfus'e,'of atleast 7.5 pounds.

In another series attests; thecatalyst; containeuningf'methyl cellulose was compared with an modified control catalyst to determine the per cent conversion ,of ethylbenzene to styrene'at' identical operating temperaturesof 610 .0. They data'aretabulated below, andshow the advantage of, the pellets made using. methyl c uumse.

Control 'C on'stltuents" Methylce'llnl6sK2600'ccntipoiSes)... 0.0 10.0 Potassium carbonat 2.8' 29 Potassium dichroni 10.8 10.4 Cement. 11.4 11.2 Graphite 22.0 15.0 Ferric oxide (red). 53.0 50.6 Water -c- 16.=2-- 25.9

Results:

.By-.product;percent I 2.9 2.3 Conversion tostyrene, per cen 35. 3 41. 6 Yieldofstyrene; per cent.. 87.4 89. 5'

Operatingtemperature,

In a similar manner, and withlikeadvantagf. 7.5- pellets are extruded and cut from a dehydrogen ation catalyst composition such as was'used at the Schkopau plant of I. G. Farbenindustrie,

modified to contain 6' per cent of methyl cellulose of the type whose 2 per cent solution in water at 20 C. has a viscosity of 4700 centipoises. The mixture consists of the following materials:

' Parts by weight Zinc oxide 80 Aluminum oxide Calcium oxide 5-'? Potassium hydroxide 2-3 Chromic oxide 0.5-0.7 Refractory cement binder 5-15 Methyl cellulose 6 Water -30 This mixture extrudesv well to give pellets which are strong both after baking and after use, and the operating temperature for a given conversion rate is several degrees lower than when the initial extrusion mix contained no methyl cellulose. It has been found that far better recellulose in the particular types of catalyst identlfied in the examples, but finds usefulness generally in pelleted or briquetted cracking and dehydrogenation catalysts of the many types known and used in the art, including catalysts for the dehydrogenation of paraflin hydrocarbons, cycloparafl'ins, heterocyclic compounds, alcohols, polynuclear hydro-aromatic hydrocarbons, and the like. In-tho'se cases in which the effective reaction temperature is lower than a temperature at which the methyl cellulose decomposes or is lower than a temperature at which oxygen-containing salts decompose to the catalytic oxides, the catalyst pellets or briquettes should first be heated to such decomposition temperature, preferably in a stream of steam, to activate the catalyst and to harden the pellet while making it more permeable to the reagent vapors. Thereafter, the herein-described advantages accrue to the catalyst in or just below its normal reaction temperature range. Such heated or calcined catalyst may be referred to as being in the activated condition.

We claim:

1. The method of preparing a dehydrogenation catalyst which comprises mixing the normal catalyst yielding substances for the intended reaction with from 3 to 15 per cent of their weight of a powdered methyl cellulose whose 2 per cent solution in water at room temperature has a viscosity from 2000 to 3000 centipoises, and with enough cementitious binder and water to make 6 a thick paste, forming the paste into pellets, dehydrating the pellets, and heating the dehydrated pellets'at least to the normal temperature for the intended reaction to decompose the methyl cellulose and to activate the catalyst.

2. The method of preparing a dehydrogenation catalyst which comprises mixing the normal catalyst yielding substances for the intended reaction with from 7 to 15 per cent of their weight of a methyl cellulose whose 2 per cent solution in water at room temperature has a viscosity from 2000 to 3000 centipoises, and with enough cementitious binder and water to make a thick paste, forming the paste into pellets, dehydrating the pellets, and heating the dehydrated pellets at least to the normal dehydrogenation temperature for the intended reaction to decompose the methyl cellulose and to activate the catalyst.

3. The method of preparing a dehydrogenation catalyst which comprises mixing potassium carbonate, potassium dichromate and ferric oxide with from 3 to 15 per cent of their weight of a powdered methyl cellulose whose 2 per cent solution in water at room temperature has a viscosity from 2000 to 3000 centipoises, and with enough refractory cement and water to' make a thick extrudable paste, extruding the paste as rods and cutting the rods to form pellets, dehydrating the pellets, and heating the dehydrated pellets in steam at from 600 to 650 C. to decompose the methyl cellulose and to activate the catalyst.

4. The method of preparing a dehydrogenation catalyst which comprises mixing potassium carbonate, potassium dichromate and ferric oxide with from 7 to 15 per cent of their weight of a methyl cellulose whose 2 per cent solution in wa ter at room temperature has a viscosity between 2000 to 3000 centipoises, and with enough cementitious binder and water to make a thick extrudable paste, extruding the paste as rods and cutting the rods to form pellets, dehydrating the pellets, and heating the dehydrated pellets in steam at from 600 to 650 C. in the presence of ethylbenzene vapors, to decompose the methyl cellulose and to activate the catalyst.

JAMES LAWRENCE AMOS. LLOYD H. SILVERJNAIL. FREDERICK J. SODERQUIST.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS The New Methocel, Powdered Dow Methylcellulose, pub. Dow Chem. Co., Midland, Mich., March 1, 1949. 

3. THE METHOD OF PREPARING A DEHYDROGENATION CATALYST WHICH COMPRISES MIXING POTASSIUM CARBONATE, POTASSIUM DICHROMATE AND FERRIC OXIDE WITH FROM 3 TO 15 PER CENT OF THEIR WEIGHT OF A POWDERED METHYL CELLULOSE WHOSE 2 PER CENT SOLUTION IN WATER AT ROOM TEMPERATURE HAS A VISCOSITY FROM 2000 TO 3000 CENTIPOISES, AND WITH ENOUGH REFRACTORY CEMENT AND WATER TO MAKE A THICK EXTRUDABLE PASTE, EXTRUDING THE PASTE AS RODS AND CUTTING THE RODS TO FORM PELLETS, DEHYDRATING THE PELLETS, AND HEATING THE DEHYDRATED PELLETS IN STEAM AT FROM 600* TO 650* C. TO DECOMPOSE THE METHYL CELLULOSE AND TO ACTIVATE THE CATALYST. 